Clarias batrachus is native to southeastern Asia and has been introduced into many places for fish farming. Walking catfish, as it is commonly known (named for their ability to move over land), is an opportunistic feeder and can go for months without food. During a drought large numbers of walking catfish may congregate in isolated pools and consume other species. They are known to have invaded aquaculture farms, entering ponds where they prey on fish stocks. C. batrachus has been described as a benthic, nocturnal, tactile omnivore that consumes detritus and opportunistically forages on large aquatic insects, tadpoles, and fish.

Clarias batrachus has a broad, flat head and an elongate body which tapers toward the tail. It is readily recognizable as a catfish with four pairs of barbels whiskers and fleshy, papillated lips. The teeth are villiform, occurring in patches on the jaw and palate. Its eyes are small. The dorsal fin is continuous and extends along the back two-thirds of the length of the body but there is no dorsal spine. The dorsal, caudal, and anal fins together form a near-continuous margin; the caudal fin is rounded and not eel-like though it is occasionally fused with the other fins. Its pectoral spines are large and robust and finely serrate along the margins with which it walks accompanied by a back and forth flexion.Their coloration is olive to dark brown or purple to black above, blue green on the sides and white below, with white specks on their rear side. C. batrachus may be easily distinguished from many of the North American Ictalurid catfishes in that the walking catfish lacks an adipose fin (Masterson, 2007; Robins, undated; GSMFC, 2006).

Notes

Clarias batrachus can survive out of water for quite sometime using its auxiliary breathing organs and move short distances over land allowing it to migrate to new water bodies (Froese and Pauly, 2009).

Lifecycle Stages

In southeast Asia, spawning period is during the rainy season, when rivers rise and fish are able to excavate nests in submerged mud banks and dikes of flooded rice fields (FishBase, 2003).

Walking catfish can be found in a variety of habitats, but they are most commonly encountered in stagnant, muddy or swampy water of high turbidity. Known to inhabit medium to large rivers, swamps, ponds, ditches, flooded fields, rice paddies, and pools left in low spots after rivers have been in flood, it is also reported to occur in intercoastal waterways of salinities up to 18 ppt. It is a tropical species with a moderate tolerance to colder waters with a reported a lower lethal temperature of 9.8°C. During cold dry months, walking catfish burrow into the sides of ponds and streams where they remain dormant until the spring rains begin (Masterson, 2007; FishBase, 2003; GSMFC, 2006).

Reproduction

Clarias batrachus engages in mass spawning migrations in late spring and early summer. Inundated rice paddy fields have been reported as favored spawning grounds over its native range. The pair manifests the 'spawning embrace' which is widely observed in other catfish species. Mating occurs repeatedly for as long as 20 hours. The pair gently nudge each other in the genital region and flick their dorsal fins; male wraps his body around the female, then the female releases a stream of hundreds to thousands of adhesive eggs into the nest or on submerged vegetation. Males guard the nests and embryos hatch in about 30 hours. Both parents guard fry for about three days, when they develop barbles visible to the naked eye and swim freely (GSMFC, 2006; FishBase, 2009, Ros, 2004c).

Introduced into Hong Kong from Thailand for aquaculture, (FishBase, 2003).The walking catfish was imported to Florida, reportedly from Thailand, in the early 1960s for the aquarium trade (Courtenay et al. 1986).

Clarias batrachus in South Florida are known to invade commercial aquaculture facilities, often consuming vast numbers of the stocks of fishes (Robins, undated). The impacts from this opportunist feeder are probably most pronounced in small, isolated wetland ponds where walking catfish quickly consume or outcompete other resident populations to become the dominant species in the pond. Resident centrarchids (freshwater sunfish) and native catfish species appear particularly susceptible to impacts from this invader (Masterson, 2007). C. batrachus can also negatively impact native amphibian populations by preying on tadpoles. The ability of walking catfish to exploit isolated, ephemeral water bodies allows them to access tadpole prey stocks that other fish cannot reach (Masterson, 2007).

Management Info

Preventative measures: Outside of its native range, numerous countries have banned possession of the Clarias batrachus, including the United States, which has classified all members of the family Clariidae as injurious wildlife which are illegal to possess without a federal permit (Robins, undated).

Informations on Clarias batrachus has been recorded for the following locations. Click on the name for additional informations.

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Clarias batrachus in South Florida are known to invade commercial aquaculture facilities, often consuming vast numbers of the stocks of fishes (Robins, undated). The impacts from this opportunist feeder are probably most pronounced in small, isolated wetland ponds where walking catfish quickly consume or outcompete other resident populations to become the dominant species in the pond. Resident centrarchids (freshwater sunfish) and native catfish species appear particularly susceptible to impacts from this invader (Masterson, 2007). C. batrachus can also negatively impact native amphibian populations by preying on tadpoles. The ability of walking catfish to exploit isolated, ephemeral water bodies allows them to access tadpole prey stocks that other fish cannot reach (Masterson, 2007).

Preventative measures: Outside of its native range, numerous countries have banned possession of the Clarias batrachus, including the United States, which has classified all members of the family Clariidae as injurious wildlife which are illegal to possess without a federal permit (Robins, undated).

Centre for Environment, Fisheries & Aquaculture Science (CEFAS)., 2008. Decision support tools-Identifying potentially invasive non-native marine and freshwater species: fish, invertebrates, amphibians.Summary: The electronic tool kits made available on the Cefas page for free download are Crown Copyright (2007-2008). As such, these are freeware and may be freely distributed provided this notice is retained. No warranty, expressed or implied, is made and users should satisfy themselves as to the applicability of the results in any given circumstance. Toolkits available include 1) FISK- Freshwater Fish Invasiveness Scoring Kit (English and Spanish language version); 2) MFISK- Marine Fish Invasiveness Scoring Kit; 3) MI-ISK- Marine invertebrate Invasiveness Scoring Kit; 4) FI-ISK- Freshwater Invertebrate Invasiveness Scoring Kit and AmphISK- Amphibian Invasiveness Scoring Kit. These tool kits were developed by Cefas, with new VisualBasic and computational programming by Lorenzo Vilizzi, David Cooper, Andy South and Gordon H. Copp, based on VisualBasic code in the original Weed Risk Assessment (WRA) tool kit of P.C. Pheloung, P.A. Williams & S.R. Halloy (1999). The decision support tools are available from: http://cefas.defra.gov.uk/our-science/ecosystems-and-biodiversity/non-native-species/decision-support-tools.aspx [Accessed 13 October 2011] The guidance document is available from http://www.cefas.co.uk/media/118009/fisk_guide_v2.pdf [Accessed 13 January 2009].

FishBase, 2003. Species profile Clarias batrachus Walking catfishSummary: FishBase is a global information system with all you ever wanted to know about fishes . FishBase on the web contains practically all fish species known to science. FishBase was developed at the WorldFish Center in collaboration with the Food and Agriculture Organization of the United Nations (FAO) and many other partners, and with support from the European Commission (EC). Since 2001 FishBase is supported by a consortium of seven research institutions. You can search on Search FishBase This species profile is available from: http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=3054&genusname=Clarias&speciesname=batrachus

Gulf States Marine Fisheries Commission (GSMFC), 2003. Clarias batrachus.Summary: Includes features, similar species, biology, maximum size, distribution (native range and in the Gulf of Mexico), interest to fisheries, current status in the Gulf of Mexico Ecosystem, impacts and references. Available from: http://nis.gsmfc.org/nis_factsheet.php?toc_id=181 [Accessed 14 August 2006].

Ros, W. 2006. Pair behaviour of the �Walking Catfish�, Clarias batrachusSummary: Available in English from: http://www.scotcat.com/articles/article83.htm In Russian from: http://vitawater.ru/aqua/fish/papers/authors/clarias21.shtml and http://vitawater.ru/aqua/fish/papers/authors/clarias22.shtml In German from http://www.welse.net/SEITEN/clarias2.htm [Accessed August 2006]